BakFlip Tonneau Cover Drainage

[icetime]

Newbie here. Just picked up my 1st GMC Sierra ('14) and put a BakFlip Fibermax tonneau cover on. I also just had the dealer add the drop in bed-liner. Question: the BakFlip has 2 drainage tubes, one for each rail, for whatever moisture they collect in the rain (car wash, etc.). However, the bed-liner has all the prior hooks and caps covered with secondary rubber 'portholes', that can be removed and access restored to the original bed. But can I please get some advice on where to route these two drainage tubes? Where does the stock bed drain from? I'm not yet familiar with the 'caps' in the original bed and what is behind them, could these be used, for example?

Any advice much appreciated.

Thanks in advance,
- ice